There is a growing need in communications and other applications for redirecting the light from an optical fiber into one or more other fibers on a selective basis. There are a number of commercially available devices which address this need. One of these devices, shown in FIG. 1, utilizes graded-index (GRIN) lenses to form a realignable image relay. Light from an input fiber 102 is collimated by a first GRIN lens 104, which is received by a GRIN lens 106 operative to focus the collimated beam onto an output fiber 108. The input lens 104 is then mechanically repositioned in alignment with other output lenses and fibers 106'-106'" and 108'-108'", respectively, to perform a sequential input-to-output switching function.
One problem associated with the arrangement just described is that each fiber must be held in place relative to its respective GRIN lens through bonding, for example, within an alignment tube. As such, an adhesive is often used between the fiber and the lens, which can degrade under high laser power, thereby adversely affecting performance. In some designs, adhesives are not used in the gap between a particular fiber and its associated GRIN lens, but outgassing from adhesives in close proximity may coat the optical surfaces, causing the same type of problem to occur.
Another existing approach involves alignment of the fiber end faces directly, without the use of bonded lenses. In this case, the fiber end faces are cleaved and polished, and brought to within a few microns and aligned center-to-center. The principle challenge with this approach is the extreme mechanical precision required in the alignment process, such that very small amounts of contamination between the fibers greatly affects performance. In addition, in both of the techniques just described, the fibers are integral to the switch, thereby making removal, reconfiguration and maintenance of the fibers difficult to achieve.